Edwin F. Hilinski
Applications are now being accepted for our Summer National Science Foundation - Research Experiences for Undergraduates (NSF-REU) Program: Sunshine Institute for the Interaction of Light with Matter
Research Interests: Mechanistic studies of photochemical and thermal reactions of organic compounds in solution; picosecond laser spectroscopy; photoinduced phenomena in the solid state.
Many important phenomena that interact to determine the outcome of a chemical reaction occur in the time regime from 10-12 to 10-6 seconds. These dynamic processes include electron and energy transfer, bond dissociation and formation, unimolecular rearrangement, diffusion, and interactions between reactants and between reactant and solvent. Our research primarily focuses on studies of reacting organic molecules and interactions that they have with their environment. A method on which we rely is picosecond laser spectroscopy. Intermediates whose lifetimes are as short as 10 ps can be generated and detected via absorption or emission spectroscopy. We synthesize compounds designed to reveal mechanistic intricacies when probed spectroscopically.
Several researches are highlighted here:
(1) Photodissociations of sigma bonds in organic molecules in solution often give fragments formally resulting from bond homolysis and bond heterolysis. We are investigating the paths of deactivation from an initially populated pi,pi* excited state leading to the production of radicals and ions. A variety of possibilities are outlined in Scheme I. The fragments that are formed also permit studies of their ground-state reactivities.
(2) The twisted excited singlet state (1p*) of a polyarylalkene may be considered to be composed of contributions from zwitterionic (I), singly (II), and doubly (III) excited states. Our time-resolved spectroscopic studies have provided evidence for the assignment of the zwitterionic form (I) as the dominant electronic contributor to the lowest 1p* of several substituted tetraphenylethenes. Substituted polyarylethenes are under investigation to evaluate the contributions of I, II, and III to 1p*.
(3) The excited-state reactivity of transient species in the subnanosecond time domain via time-resolved spectroscopy is an area that we are investigating with the three-pulse laser system that we developed.
(4) Photoinduced electron transfer, involving excitation of ground-state organic electron donor-acceptor complexes, is being studied to learn the roles of orbital symmetries and the effects of heavy atoms on electron-transfer rates in solution.
(5) Photophysical phenomena associated with semiconducting and superconducting materials are under investigation through several collaborations.
In our research, we strive to learn how electrons are apportioned in these processes and how our results compare with theoretical predictions.
Hilinski, E. F, "The Picosecond Realm," in Reactive Intermediate Chemistry, Moss, R. A.; Platz, M. S.; Jones, M., Jr., Eds., Wiley-Interscience, New York, 2004, p. 873.
Takahashi, Y.; Ohaku, H.; Nishioka, N.; Ikeda, H.; Miyashi, T.; Gormin, D. A.; Hilinski, E. F., "Charge-Transfer Excitation of Electron Donor-Acceptor Complexes of Arylcyclopropanes," J. Chem. Soc., Perkin Trans. 2 1997, 303.
Hilinski, E. F.; McGowan, W. M.; Sears, D. F., Jr.; Saltiel, J., "Evolutions of Singlet Excited-State Absorption and Fluorescence of all-trans-1,6-Diphenyl-1,3,5-hexatriene in the Picosecond Time Domain," J. Phys. Chem. 1996, 100, 3308.
McGowan, W. M.; Hilinski, E. F., "Competitive Bond Homolysis and Intersystem Crossing in the Picosecond Time Regime. Photodissociation of 9-Bromo- and 9-Chlorofluorene in Cyclohexane," J. Am. Chem. Soc. 1995, 117, 9019.
Gao, F.; Dharia, J. R.; McGowan, W. M.; Hilinski, E. F.; Johnson, K. F.; Schlenoff, J. B., "New Fluors for Radiation-Tolerant Scintillators," Mater. Res. Soc. Symp. Proc. 1994, 348, 173.
Tate, K. L.; Hilinski, E. F.; Foster, S. C., "Angle-Dependent Laser-Induced Voltages in Room-Temperature Polycrystalline Wafers of YBa2Cu3O7-x," Appl. Phys. Lett. 1990, 57, 2407.
Schmidt, J. A.; Hilinski, E. F., "Concurrent Pump-Probe and Streak Camera Measurements with a Single Mode-Locked Nd:YAG Laser. A Picosecond Absorption/Emission Spectrometer," Rev. Sci. Instrum. 1989, 60, 2902.
Mecklenburg, S. L.; Hilinski, E. F., "Picosecond Spectroscopic Characterization of the 9-Fluorenyl Cation in Solution," J. Am. Chem. Soc. 1989, 111, 5471.
Schmidt, J. A.; Hilinski, E. F., "Evolution of Electronically Excited Triphenylmethyl Radical. Picosecond Preparation-Pump-Probe Spectroscopic Experiments," J. Am. Chem. Soc. 1988, 110, 4036.
Schilling, C. L.; Hilinski, E. F., "Dependence of the Lifetime of the Twisted Excited Singlet State of Tetraphenylethylene on Solvent Polarity," J. Am. Chem. Soc. 1988, 110, 2296.